This research involves the use of nuclear magnetic resonance for the study of secondary and tertiary structure of transfer RNA. We are using proton nmr chemical shifts and relaxation times of modified base methyl and methylene groups as probes of structure and dynamics. Using several purified tRNA's from E. coli we will be exploring the interaction of the TPsiC and dihydrouridine loops, the effect of Mg (II) binding on tertiary structure stability and dynamics, the codon-anticodon interaction, and tertiary structure in aminoacyl tRNA. We plan to fractionate tRNA whose uridines are substituted for 5-fluorouridine. Fluorine-19 nmr will then provide a new method for examining tRNA in solution, particularly the dynamical aspects of structure. Part of our work will be devoted to expanding the utility of proton nmr for tRNA studies. We are exploring ways in which the region from -5 to -9 ppm from DSS can be resolved into single proton resonances.